Pressed-formed paperboard containers, in particular, plates, are known in the art. See generally U.S. Pat. No. 6,715,630 to Littlejohn et al, which disclosure is incorporated herein in its entirety by this reference. Such plates are typically formed by pressing paperboard in a heated matched metal die set. Surface temperatures in the mold are typically on the order of about 300° F. and above and the plates are formed under high pressure to provide permanent shape and strength to a product that typically comprises pleats on the sidewalls and rims. The pleats comprise integrated fibrous structures formed from multiple paperboard layers under heat and pressure such that the pleats are generally inseparable into their constituent layers when the plate is being used. Examples of such pressboard plates are sold by the assignee of the present invention under the tradenames DIXIE® and DIE ULTRA®.
Other types of disposable plates formed from paper can be formed from a slurry of pulp. Such a slurry is molded to provide a paperboard plate. An example of such a pulp-molded product is sold as by the Huhtamaki Corporation as CHINET®.
Such pressboard and pulp-molded paper plates have achieved widespread acceptance in the marketplace. However, these types of plates are considered to be “premium” products and are generally used by persons who desire a high-end product. Specifically, these plates generally are priced several times more than so-called “economy plates.”
Another type of disposable plate is typically used by persons who desire a lower cost disposable paperboard plate. Such plates are fluted “economy” plates, also known as “white no-print” plates (“WNP plates”). WNP plates are formed by simultaneously pressing from 2 to 5 layers of paperboard at a time. Prior art WNP plates exhibit a fluted pattern in their rim area to take up the extra material during formation due to the reduction in perimeter of the plate into the final product resulting from material gathering.
Prior art WNP plates currently make up a significant portion of the market for paper plates because of their significantly lower cost than the so-called “premium” plates discussed previously. In particular, this market segment has been estimated to be up to 60% of disposable plate market volume. Prior art WNP plates are commonly formed with about 100 pounds per ream uncoated paperboard or from about 150 to about 170 pounds per ream clay coated paperboard.
Referring to FIG. 1 herein, a prior art WNP plate (that is, a WNP plate made using prior art pressing processes) is shown. In this Figure, plate 10, which includes a bottom 12, a center transition 14, a lower sidewall transition 16, a fluted sidewall 18, an upper sidewall transition 20, and an outer pleated shelf 22. These plates are typically prepared from a stack of pre-cut paperboard blanks under pressure in a matched metal die set. However, because of the high temperatures and pressures used in forming, prior art WNP plates can often be difficult to separate, especially when interlayer pleating or folding of the plates occurs during the pressing process. As would be readily recognized by anyone who has used WNP plates, it is very frequently difficult to remove a single plate from a stack of plates because the individual plates stick together. This leads to waste since multiple plates are used when only one is required. Thus, even though on an individual basis the plates are less expensive than so-called “premium plates,” as used, prior art WNP plates can approach the cost of the more expensive plates if 2 or 3 or more plates cannot be separated for individual use.
The inventors herein have discovered a punch-through die forming process that provides an improved method for preparing WNP plates such that the plates are less likely to stick together. The method of the present invention also provides a more efficient manufacturing process wherein time, materials and energy can be saved in the manufacture of the WNP plates of the present invention. A paperboard material having a treatment making the resulting plates water, grease or oil resistant can also be used in the invention herein. A new type of WNP plates and stacks thereof are formed by the processes of the present invention.